An equalizer of the type here considered is the subject matter of commonly owned U.S. Pat. No. 4,288,872 in the name of one of us, Giovanni Tamburelli. As disclosed in that patent, the equalizer comprises two parallel branches inserted between a source of incoming pulse samples, representing binary symbols received with a predetermined recurrence period, and a decision unit. The first branch has an upstream filter for the linear suppression of postcursor effects, followed by a nonlinear compensation cell of feed-forward type purging the incoming symbols from precursor interference. Analogously, an upstream filter in the second branch linearly suppresses precursor effects and is followed by a nonlinear compensation cell of feedback type designed to eliminate postcursor interferences.
The operation of that equalizer is based on the presumption that decision errors are unlikely to occur simultaneously in both branches; the summing of the output signals of these branches reduces possible distortions due to the occurrence of one such error.
Although the system of the prior patent generally performs satisfactorily, there is still the risk that consecutive decision errors in one branch may falsify the final output signal.